1. Field of the Invention
The present invention relates to a multilayer printed circuit board which can be used for optical communications.
2. Discussion of the Background
In recent years, together with the expansion of high speed Internet networks, it has been suggested that optical communications be used in communication between trunk networks and terminal equipments (personal computers, mobile units, games and the like), communication between terminal equipments and communication within terminal equipment, in addition to communication within trunk networks.
In trunk networks, increase in the speed of switching apparatuses, such as address translators and routers, is progressing, together with increase in the amount of information, and therefore, transmission of signals between a daughter board and a switching board in, for example, bookshelf type backplane boards through optical communication has been examined, and optical communication through optical fibers using optical connectors has been examined (see JP-A 1999-113033).
In addition, provision of an optical transceiver in terminal equipment allowing optical communication through optical fibers has also been examined.
The contents of JP-A 1999-113033 are incorporated herein by reference in their entirety.
Electronic parts are mounted on the two surfaces of printed circuit boards used as a daughter board and inside terminal equipment, in order to achieve higher performance and miniaturization of switching apparatuses and terminal equipment in printed circuit boards, and furthermore, miniaturization and increase in the density of mounting of electronic parts are achieved together with increase in the number of mounted parts.
In addition, in the case where optical communication through optical fibers is used, as described above, an optical connector is mounted in the periphery of an end portion of the printed circuit board which forms, for example, a daughter board, and furthermore, this optical connector is connected to a photoelectric conversion element mounted on the printed circuit board. In addition, an optical transceiver is also provided to terminal equipment, usually in such a state as to be mounted on a multilayer printed circuit board.
Thus, it has become necessary for optical connectors and photoelectric conversion elements and optical transceivers to be mounted on a printed circuit board, and in this case, it is necessary to secure a new space for mounting on a printed circuit board, causing a problem that the printed circuit board increases in size, and furthermore, connection with an optical fiber is required and the location in which this is mounted is limited to the periphery of an end portion of the printed circuit board, and as a result, a problem arises that there is less freedom in design.
Thus, as a result of diligent examination, the present inventors found that optical circuits may be formed inside a multilayer printed circuit board in order to achieve miniaturization of the printed circuit board for achieving miniaturization of terminal equipment and the like, and increase the freedom in design, and completed the present invention.